lib: add sbuf

Signed-off-by: Christian Franke <chris@opensourcerouting.org>

lib/sbuf.c

@@ -0,0 +1,107 @@
+/*
+ * Simple string buffer
+ *
+ * Copyright (C) 2017 Christian Franke
+ *
+ * This file is part of FRR.
+ *
+ * FRR is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2, or (at your option) any
+ * later version.
+ *
+ * FRR is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with FRR; see the file COPYING.  If not, write to the Free
+ * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+ * 02111-1307, USA.
+ */
+#include <zebra.h>
+
+#include "sbuf.h"
+#include "memory.h"
+
+void sbuf_init(struct sbuf *dest, char *buf, size_t size)
+{
+	dest->fixed = (size > 0);
+	if (dest->fixed) {
+		dest->buf = buf;
+		dest->size = size;
+	} else {
+		dest->buf = XMALLOC(MTYPE_TMP, 4096);
+		dest->size = 4096;
+	}
+
+	dest->pos = 0;
+	dest->buf[0] = '\0';
+}
+
+void sbuf_reset(struct sbuf *dest)
+{
+	dest->pos = 0;
+	dest->buf[0] = '\0';
+}
+
+const char *sbuf_buf(struct sbuf *buf)
+{
+	return buf->buf;
+}
+
+void sbuf_free(struct sbuf *buf)
+{
+	if (!buf->fixed)
+		XFREE(MTYPE_TMP, buf->buf);
+}
+
+void sbuf_push(struct sbuf *buf, int indent, const char *format, ...)
+{
+	va_list args;
+	int written;
+
+	if (!buf->fixed) {
+		char dummy;
+		int written1, written2;
+		size_t new_size;
+
+		written1 = snprintf(&dummy, 0, "%*s", indent, "");
+		va_start(args, format);
+		written2 = vsnprintf(&dummy, 0, format, args);
+		va_end(args);
+
+		new_size = buf->size;
+		if (written1 >= 0 && written2 >= 0) {
+			while (buf->pos + written1 + written2 >= new_size)
+				new_size *= 2;
+			if (new_size > buf->size) {
+				buf->buf =
+					XREALLOC(MTYPE_TMP, buf->buf, new_size);
+				buf->size = new_size;
+			}
+		}
+	}
+
+	written = snprintf(buf->buf + buf->pos, buf->size - buf->pos, "%*s",
+			   indent, "");
+
+	if (written >= 0)
+		buf->pos += written;
+	if (buf->pos > buf->size)
+		buf->pos = buf->size;
+
+	va_start(args, format);
+	written = vsnprintf(buf->buf + buf->pos, buf->size - buf->pos, format,
+			    args);
+	va_end(args);
+
+	if (written >= 0)
+		buf->pos += written;
+	if (buf->pos > buf->size)
+		buf->pos = buf->size;
+
+	if (buf->pos == buf->size)
+		assert(!"Buffer filled up!");
+}

lib/sbuf.h

@@ -0,0 +1,77 @@
+/*
+ * Simple string buffer
+ *
+ * Copyright (C) 2017 Christian Franke
+ *
+ * This file is part of FRR.
+ *
+ * FRR is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2, or (at your option) any
+ * later version.
+ *
+ * FRR is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with FRR; see the file COPYING.  If not, write to the Free
+ * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+ * 02111-1307, USA.
+ */
+#ifndef SBUF_H
+#define SBUF_H
+
+/*
+ * sbuf provides a simple string buffer. One application where this comes
+ * in handy is the parsing of binary data: If there is an error in the parsing
+ * process due to invalid input data, printing an error message explaining what
+ * went wrong is definitely useful. However, just printing the actual error,
+ * without any information about the previous parsing steps, is usually not very
+ * helpful.
+ * Using sbuf, the parser can log the whole parsing process into a buffer using
+ * a printf like API. When an error ocurrs, all the information about previous
+ * parsing steps is there in the log, without any need for backtracking, and can
+ * be used to give a detailed and useful error description.
+ * When parsing completes successfully without any error, the log can just be
+ * discarded unless debugging is turned on, to not spam the log.
+ *
+ * For the described usecase, the code would look something like this:
+ *
+ * int sbuf_example(..., char **parser_log)
+ * {
+ *         struct sbuf logbuf;
+ *
+ *         sbuf_init(&logbuf, NULL, 0);
+ *         sbuf_push(&logbuf, 0, "Starting parser\n");
+ *
+ *         int rv = do_parse(&logbuf, ...);
+ *
+ *         *parser_log = sbuf_buf(&logbuf);
+ *
+ *         return 1;
+ * }
+ *
+ * In this case, sbuf_example uses a string buffer with undefined size, which will
+ * be allocated on the heap by sbuf. The caller of sbuf_example is expected to free
+ * the string returned in parser_log.
+ */
+
+struct sbuf {
+	bool fixed;
+	char *buf;
+	size_t size;
+	size_t pos;
+	int indent;
+};
+
+void sbuf_init(struct sbuf *dest, char *buf, size_t size);
+void sbuf_reset(struct sbuf *buf);
+const char *sbuf_buf(struct sbuf *buf);
+void sbuf_free(struct sbuf *buf);
+#include "lib/log.h"
+void sbuf_push(struct sbuf *buf, int indent, const char *format, ...)
+	PRINTF_ATTRIBUTE(3, 4);
+
+#endif

lib/subdir.am

@@ -51,6 +51,7 @@ lib_libfrr_la_SOURCES = \
 	lib/ptm_lib.c \
 	lib/qobj.c \
 	lib/routemap.c \
+	lib/sbuf.c \
 	lib/sha256.c \
 	lib/sigevent.c \
 	lib/skiplist.c \
@@ -125,6 +126,7 @@ pkginclude_HEADERS += \
 	lib/qobj.h \
 	lib/route_types.h \
 	lib/routemap.h \
+	lib/sbuf.h \
 	lib/sha256.h \
 	lib/sigevent.h \
 	lib/skiplist.h \